The present invention relates to a host controller apparatus that causes a processor to execute an event related to event information recorded in a system memory by outputting an interrupt signal to the processor.
A host apparatus connected to a universal serial bus (USB) device includes a USB host controller therein in order to control communication with the USB device. The host apparatus includes a notebook personal computer (hereinafter referred to as a notebook PC) or the like. Since the notebook PC may be operated using a battery, power saving is required. Accordingly, reduction in power consumption is required also in the USB host controller mounted on the notebook PC.
Japanese Unexamined Patent Application Publication No. 2003-202943 discloses detecting whether a USB device connected to a built-in slot of a host apparatus is used, and stopping output of an interrupt signal to a CPU regarding the USB device when the USB device is not used. Accordingly, it is possible to achieve reduction of power consumption of a host controller.
Japanese Unexamined Patent Application Publication No. 2009-093418 discloses that a USB host controller specifies an endpoint that requires data transfer to perform data transfer only to the endpoint that is specified. Accordingly, power consumption is expected to be reduced compared to a case in which data transfer is performed to all the endpoints that are set. The endpoint is a transferring buffer used to perform data transfer in a USB system bus.
Japanese Unexamined Patent Application Publication No. 11-194847 discloses selecting one of a system reset signal and a resume reset signal, and supplying the selected signal to a USB host controller. The system reset signal is a signal to reset the whole computer system when a power supply to the computer system is initially turned on. The resume reset signal is a signal generated when the mode is returned to a normal state from a suspend state, and is a signal to reset a device whose power is OFF due to the suspend state. By switching these signals, the state can be returned to a normal state by using the resume reset signal when the power supply of the USB host controller is OFF. Accordingly, low power consumption of the USB host controller may be achieved.
As described above, various techniques are used to achieve power saving of the USB host controller.
Extensible Host Controller Interface for Universal Serial Bus (xHCI) Revision 1.0, Intel Corporation, May 21, 2010 discloses that an extensible Host Controller Interface for Universal Serial Bus (xHCI)-compliant USB host controller updates Event Ring on a system memory upon occurrence of events. For example, the events include changes of connection status due to disconnection of a USB device connected to Down Port, for example. After updating the Event Ring, the USB host controller outputs an interrupt notification to a CPU to request processing. However, a predetermined time interval defined by Interrupt Moderation (hereinafter referred to as an IMOD) needs to be provided between outputs of the interrupt notification from the USB host controller to the CPU. Accordingly, the USB host controller outputs the interrupt notification after a lapse of IMOD time when IMOD time does not elapse after the output of the previous interrupt notification.